In recent years, PET-MRI apparatuses having a combination of positron emission tomography (PET) apparatuses and magnetic resonance imaging (MRI) apparatuses have been made into products. Generally, the PET-MRI apparatuses are realized by attaching PET detectors to the MRI apparatuses, and in many cases, the positions of the PET detectors are fixed. However, when the PET detectors are fixed in the vicinity of magnetic field centers of the MRI apparatuses, the PET detectors may interfere with high power radio frequency (RF) magnetic fields generated in the magnetic field centers and radio frequency coils (RF coils) detecting generated magnetic resonance signals, which may cause data acquisition not to be properly made.